Various hematology analyzers are commercially available, from the high end, high capacity and high speed, fully automated instruments in hospitals to the low end, small counter top instruments for doctor's offices. Almost all of these instruments have multiple reagents and cleaner on board for automated sample preparation and measurements on the instruments. Although these hematology analyzers have known advantages of high capacity, batch sample analysis, automated sample aspiration and preparation, and automated cleaning cycles, these instruments are relatively high cost and use large quantity of reagents, which requires high maintenance of the instruments and reagent inventory management. Therefore, it is difficult to adapt these instruments in a near-patient test environment, such as in the emergency room, where minimum maintenance, minimum personal training and operator skill are required.
In the recent years, disposable cassette containing reagents for one sample analysis and blood analyzers adapted to use the disposable cassettes have been developed for meeting such a need in near-patient testing.
U.S. Pat. No. 7,335,339 discloses a disposable cassette which has a turning valve for sampling or isolation blood for different measurements and two cylinders containing pre-filled reagents for blood analysis. Mixing of the reagent with a blood is affected by a piston located in each cylinder. The structure of the cassette is complex and it is costly to manufacture. In this cassette, the pre-filled reagents are separated from other parts of the cassette by the turning valve, which is a moving component itself. The cassette does not contain a cleaner and the measurement devices on the instrument are cleaned by a cleaning solution provided to the instrument.
WO 2004/045770 A1 discloses a disposable cassette, which includes multiple receptacles formed by depressions of a surface of the housing and sealed by a diaphragm, and multiple channels interconnecting selected receptacles. Two receptacles of the cassette contain a diluent, one receptacle contains a hemolysis agent, and another receptacle contains a cleaner, respectively. The cassette has an elongated hole adapted to receive a capillary holder specially designed to use with the cassette for receiving and holding a capillary tube or micropipette that is used to deliver a blood into the cassette. A portion of a blood is segmented by a sliding valve to mix with a first diluent to form a first diluted blood, then two portions of the diluted sample are segmented by the sliding valve, one is mixed with the second diluent to form a second diluted sample mixture for red blood cell measurement, and another is mixed with the hemolysis agent to form a lysed sample mixture for white blood cell measurement. The second diluted sample and the lysed sample mixture are withdrawn from the cassette through needles penetrating through sealed openings on two opposing sides of the cassette into a blood analyzer.
Despite the advantages of this cassette in its simple method of mixing by alternately applying a pressure on selected receptacles, it has several disadvantages rendering it difficult to use. This cassette lacks secure sealing of the liquid reagents during transportation. The liquid reagents are restricted from flowing into other sections only by the sliding valve, which itself is a moving component. The liquid reagents can easily leak out from the interface with the sliding valve, causes potential chemical contaminations to sliding valve that supposedly separates different portions of a blood to different reagents, and causes errors of the measurements, because the pre-filled reagents determine the ratio of a dilution and ultimately the concentrations of the blood cells to be measured.
Furthermore, this cassette requires two sequential steps of dilution, therefore, it consumes more diluent, and takes longer time to prepare the sample mixtures. As can be appreciated, accuracy of the measurements depends not only on the second step of mixing, but also on the completion and quality of mixing in the first dilution. Moreover, this cassette requires a special tool, the capillary holder, for filling the blood, which also increases the overall time for preparing the sample, as it requires operator to insert a glass capillary tube into the holder for each blood to be tested. It also increases the risk of injury, because the thin glass tube can be fractured when it is not aligned properly during insertion, and increases operator's exposure to bio-hazard materials. Additionally, this cassette requires a complex interface of the blood analyzer. Because withdrawing the sample mixtures is from two opposing sides of the cassette, the cassette has to be in a horizontal position with the device of applying pressures positioned above the cassette and the devices withdrawing the sample mixtures on both sides. Because of this structure, it is also difficult to avoid potential withdrawing air bubbles into the conduits connecting to the cell counting devices.
Therefore, it is desirable to provide an improved disposable cassette that ensures sealing of the reagents contained in the cassette during storage and transportation to prevent cross-contaminations within the device and to improve accuracy of the blood measurements. It is further desirable to have a cassette that provides a single step dilution for preparing sample mixtures for both red blood cell and white blood cell measurements with a simple process and shorter preparation time. Moreover, it is desirable to provide a cassette that can be supported by a simple interface of a blood analyzer. Furthermore, it is desirable to provide a cassette that is convenient and safe to use by the operators, and requires minimum training and skill.